It's not about liking opinions or not. It's about running suboptimal sets to try and check a Pokemon in response to people complaining said Pokemon lacks reliable counterplay. You can run anything you want, but don't pretend that it's suddenly a reasonable suggestion to make to others to run. Scarf Valiant in the current metagame isn't that great, it would much rather nuke or have the ability to switch around options.
And I'd rather not have a waste of an item slot on a one-time use item that wears off after switching out/being forced out.
Oh look, I used my Booster Energy to up my speed! Now they swapped into something that hard checks me and I have to switch out, losing my speed boost! Now I'm just a normal ass, normal Iron Valiant that has no item anymore!
Seriously, even Focus Sash is a better item. The only Pokemon that can fully make use of is Roaring Moon, Iron Bundle (because it has no solid checks), and DEBATABLY Iron Moth.
Roaring Moon doesn't mind being forced out after a Booster proc because it'll both have Acrobatics boosted, and have Dragon Dance in its kit to get that speed back later. Valiant has neither of these things.
Iron Bundle makes great use of it (even if it is banned) because there was basically no solid checks to it. Gastro/Clod with Tera Steel was your best option, and even that wasn't great.
Iron Moth makes use of it because Moth doesn't get anything good for boosting. You get Agility, whoopee.
Band, Specs, Scarf, Sash, Life Orb, and Expert Belt are all leagues better than Energy Booster on Valiant. That's my opinion on it, that's where it will stay.
you know I gave it some thought. What exactly switches into Choice Band Roaring Moon in Sun (+Atk) well?
This occurs more commonly with Walking Wake around, just food for thought.
I mean Corviknight can, but it HATES coming in a banded Crunch.